12/12 broken cycle : What to do now to shock the girls as little as possible?

Don't worry, 1 hour might be OK - they need a minimum of 10 hours of darkness each night unbroken to flower, so 11 hours should be ok. That said, as you clearly know already, you are risking confusing the plants body clock each time you change the number of light hours. With that in mind, keep an eye out for problems now - specifically hermie male flowers - and don't do it again! 😊 Good luck!